Variable electric resistance device



Inventor: John SZmmeT';

His Attorney.

J S ZIMMER VARIABLE ELECTRIC RESISTANCE DEVICE Filed Dec. 22, 1949 Feb. 13, 1951 Patented Feb. is, 1951 VARIABLE ELECTRIC RESISTANCE DEVICE John S. Zimmer, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application December 22, 1949, Serial No. 134,471

9 Claims.

My invention relates to variable electric resistance devices, and more particularly to automatic resistance regulators actuated in response to a controlling quantity, such as current, voltage, pressure, liquid level, or the like. The present invention is especially well adapted for use as a resistance regulator connected to control aircraft electrical equipment, where it is frequently subjected to severe shock, high values of acceleration, vibration and large changes in temperature or atmospheric pressure.

It is a general object of my invention to provide a new and novel variable electric resistance device which is substantially unaffected by shock, vibration, acceleration and changes in temperature or pressure.

It is a further object of my invention to provide a new and novel variable electric resistance device which demonstrates a wide range of resistance variation in response to a very small controlling movement.

It is a still further object of my invention to provide, in a variable electric resistance device, new and novel means for effecting a smooth and continuous resistance variation over a predetermined range.

A specific object of my invention is the provision of a new and improved curved spring pressure plate type of variable electric resistance element which ensures positive contact and pressure over a variable contact area.

In carrying out my invention in one form, I provide a first metallic plate covered with a sheet or layer of electric conducting elastomeric material, such as graphite-filled silicone rubber or the like. Attached at one end to the first plate, I provide an arcuate metallic plate having its convex surface facing inwardly and covered with a similar layer of electric conducting silicone rubber or the like. At least one of the plates is resilient and they are so connected that their free ends diverge. The conducting rubber layers or coatings serve as resistance elements, and terminals are provided to pass current between the plates and through the resistance layers across their engaging surfaces. As the-diverging ends of the plates are pressed together the area of contact between the conducting rubber layers is varied, thereby to effect a variation in resistance. In order to provide a high value of resistance at the high end of the resistance range while still maintaining an appreciable contact area, I interpose between one of the plates and its rubber covering layer, a sheet of insulating material extending from the wnnected ends of 2 the plates toward the diverging ends for only a part of the eiective contact length of the plates. A biasing spring is arranged to apply pressure to the contact spring, and a controlling electromagnet is arranged to oppose the biasing spring.

My invention will be more fully understood and its various objects and advantages further appreciated by referring now to the accompanying drawing. in which Fig. 1 is a side crosssectional view of a variable electric resistance device embodying my invention; Fig. 2 is a top cross-sectional view ol' the device shown at Fig. 1 taken along the line 2-2 ofFig. 1 and looking in the direction of the arrows; and Fig. 3 is a fragmentary cross-sectional view on an enlarged icale of the resistance elements themselves shown also at Fig. 1.

Referring now to the drawing, I have shown a resistance regulator embodying a preferred form of my inventionand comprising a hollow cylindrical casing I having an internal transverse dividing wall la. Upon one side of the wall la there are cast integrally with the casing I a plurality of parallel axially disposed cooling fins 2. To the other side of the dividing wall la there is fixed in fiatwise relation a rigid fiat plate or disk 3 made of electric conducting material such as copper, aluminum or the like. Upon the plate. 3 and at diametrically opposite sides of the plate there are positioned sectors I of insulating sheet material. The insulating sectors 4 extend radially inward for only a portion of the distance to the center of the circular plate 3. The uninsulated central area of the conducting plate 3 and the insulating sectors l are both overlayed with a sheet, or layer l of electric conducting elastomeric material which will be described more fully hereinafter.

A pair of curved resilient metallic plates or leaf springs 6 of trapezoidal configuration (Fig. 2) are connected to the plate 3 at diametrically opposite points above the insulating sectors l. The springs 6 extend radially inward toward the center of the plate in end-to-end relation. Each arcuate spring 6 is provided at its outer end with an upturned lip 6a through which it is bolted to an insulating block l mounted upon the conducting plate 3. Mounted also upon each insulating block 'l is a terminal connector 8 positionedA in contact with the associated Vspring lip 6a and having connected thereto suitable lead wires 9. The springs l are positioned with their convex surfaces facing inwardly so that they diverge from the plate l toward the free ends of the springs. Each arcuate spring C is covered on its inwardly facing convex surface with a layer or sheet of electric conducting elastomeric material Il similar to the sheet 5. The conducting sheets Il do not cover the upturned spring lips in, but are in contact with the sheet 5 at the fixed end of the springs. The elastomeric conducting layers i and Il have appreciable electric resistance and serve as resistance elements.

An electromagnetic actuating mechanism for pressing the free ends of the springs l toward the conducting plate 5 and for thus controlling the area oi contact between the resistance sheet l and the resistance sheets Il is mounted within the casing I above the springs i. To this end an internally and externally threaded mounting collar,\ or ring II is threadedly mounted within the end of the casing i above the plate I. By reason of its threaded mounting, the collar ii is axially adjustable within the casing I. The collar II is locked in any desired axial position by a plurality of locking bolts i2 (only one of which is shown) arranged circumferentially around the collar Il. The bolts I! are threaded into the collar I I and each has mounted thereon a U-shaped locking member or yoke I3 which stands astride o1 the threaded connection between the collar Il and the casing I.

Disposed above the leaf springs l, I provide an actuating plate Il having a ilat lower surface covered with a layer Ila oi.' insulating material and positioned in substantially parallel spaced relation with the upper surface of the plate 3. The actuating plate or dk Il is circular and is provided with an upwardly extending central hub IIb to which is xedly attached a circular arma# ture dan It formed of a suitable magneuzabie material. 'I'he actuating plate Il and the armature II are preferably electrically insulated from each other by suitable hanged insulating collar I l. 'I'he actuating plate and armature assembly are carried by an annular spring plate II the external periphery of which is seated in an annular recessinthecollar Il andtheinnerperipheryoi whichisseatedinanannuhrgrooveinthearmature Il. Thespring IIkarrangedtobiasthe amature and actuating plate assembly toward the conductim plate 3. thereby to press the free endsofthespringltowardtheplate I. The biasing spring i'l tly strong to overcome the oppositely exerted forces ci' the springs 8.

Mounted also upon the collar II. and externally or the casing I. I provide an electromagnet for attractingthe armature Il to oppose the biasing force of the spring I1 thereby controllingthe axialpositionofthe actuating plate il and the area of contact between the elastomeric resistance layers l and Il. The electromagnet comprises a cup-shaped magnetizable housing Il andanaxiai oorellwithinthe housing. An 2l is moimted within thehousinglltbecore I9. The coilisheldinplacebyablering or annuiuslithreadedinternallyintotheopen end oi the cup-shaped housing Il and having a circular center aperture radially spaced from the end of the core Il. The entire electromagnet assemblyisthreadedinternailyintothemounting collarlibymeansofthreadsontheoutsideof cup Il, so that the is positioned insuchawaythattheannnlarairgapbetween tbemagnetisablerlngllandtbecoreii'iscompleted through thecircular armature Il. The axialposltlonofthewithrespect` to the mounting collar II is adjustable by reason of the threaded mounting. The eiectromagnet is locked in a desired axial position in the collar ii by means of a plurality of locking bolts 22 (only one of which is shown) located circumferentially around the collar Il. Each of the bolts 22 is threaded into the collar II and has mounted thereon a U-shaped locking member or yoke 23 which stands astride of the threaded connection between the electromagnet housing Il and the collar II.

The electric conducting elastomeric resistance material forming the resistance layers l and I. may suitably be a carbon-lled elastomer, such as natural or articial rubber, or the like (including silicone rubber). I prefer to use for the resistance elements l and Il a graphite-nlled silicone rubber (also known as a solid elastic organopolysiloxane) wherein the organic roots attached to silicon comprise essentially methyl groups. Examples of such silicone rubbers may be found in the co-pending application Serial No. 134,599 tiled December 22, 1949, concurrently herewith by Curtis S. Oliver and assigned to the same assignee as the instant application. Various silicone rubbers which may be graphite-filled and employed in accordance with ymy invention are also described and claimed in Patent 2.448.756 issued to Maynard C. Agens on September 7. 1948.

It will now be evident that in the preferred embodiment of my invention shown and described the current path through the resistance element between terminal connectors l may be followed from one terminal connector to the associated leaf spring l, through the contacting silicone rubber conducting layers Il and 5 into the conducting plate 3, then diametrically across the center of the conducting plate l and through the silicone rubber layers l and I0 into the other spring l and the connected terminal connector l. It will be apparent to those skilled in the art that by making electrical connection to the plate I, the two paths through the resistance layers l and i0 may be connected in parallel rather than in series as shown.

In operation. as the electromagnetic attraction of the armature Il is decreased and the biasing spring I1 allowed to press the springs l farther toward the plate l. the area of contact between the conducting rubber layers l and Il is increased, so that the resistance between the terminals l is decreased. Conversely, as the energizatlon of the coil Il is increased thereby to attract the armature Il with a greater force and more effectively to oppose the biasing spring i1. the actuating plate Il is raised away from the plate 3 and the arcuate contact springs l allowed to diverge from the plate I, thus reducing the area of contact between the resistance layers i and i0. As the area oi. contact is thus reduced. the resistance of the device increases to a maxin mum at the point where the free ends oi the springs 6 are under no pressure from the actuating plate i4. At this high resistance end o! the resistance range the insulating sectors 4 ensure an appreciable length of current path through the resistance layers l and Il. and thus a maximum resistance of appreciable value. It will be evident that by reason of the interposition of the insulating sectors l the current path between each terminal connector l and the conducting plate l necessarily includes a minimum radial length of the-r layer l between the terminal connector l and the radially inner end of the associated insulating sheet 4. 'It will be evident to those skilled in the art that, by selecting the insulating sheets l of any predetermined size a desired maximum resistance may be selected.

In respect to the adjustment of the device, it will be apparent that the initial pressure of the actuating plate Il against the arcuate springs l, and thus the maximum resistance value of the device, may be varied by adjusting the axial position of the mounting ring Il within the casing I and locking the ring in place by the bolts I2. Similarly, the value of the controlling force necessary to eiect a resistance change may be selected by adjusting the position of the electromagnet casing Il within the mounting ring Il, thereby to vary the airgap between the armature I5 and the core I9.

While I have shown and described by way of illustration only a preferred embodiment of my invention, many modifications will occur to those skilled in the art. For example, it will be evident that it is not necessary to the practice of my invention in its broader aspects that either of the co-acting resistance Aplates (3 and 6) be either rigid or flat. Both plates may, if desired, be arcuate so long as they are so connected that their free ends normally diverge. With lamellar plates this is ensured if the surface of greatest concavity faces outwardly. Similarly, whether one plate be iiat or whether both be curved, either one or both may be resilient. Moreover, my invention is not limited in its scope to actuation of the coatingspring pressure plates by electromagnetic means, but any suitable means for controlling the relative positions of the plates may be utilized.

Accordingly, therefore, I wish it to be understood that I intend in the appended claims to cover all modifications which fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A variable electric resistance device comprising a pair of metallic plates at least one of which has a curved surface and at least one of which is resilient, means connecting said plates together at one point in overlying diverging relation, a layer of electric conducting elastomeric material covering the inwardly facing surface of each said plate, said layers being in contacting relation at the fixed point of said plate, a layer of insulating material interposed between one said plate and its elastomeric covering layer adjacent said point and extending for only a portion of the distance between said point and one pair of proximate diverging ends of said plates, and means for pressing said proximate diverging ends together to vary the area of contact of said elastomeric conducting layers.

2. A variable electric resistance device comprising a pair of metallic plates at least one of which has a curved surface and at least one of which is resilient, means connecting said plates together at one end in overlying diverging relation, a layer of electricy conducting elastomeric material covering the inwardly facing surface of each said plat'e,.said layers being in contacting relation at the fixed ends of said plates, a layer of insulating material interposed between one said plate and its elastomeric covering layer and extending from said fixed ends toward the diverging ends of said plates for only a portion of the effective contact length of said plates, and means for pressing the diverging ends of said plates together to vary the area of contact of said elastomeric conducting layers.

3. A variable electric resistance device comrising a rigid metallic plate having a. iiat surface covered with a lever of electric conducting elastomeric material, an arcuate metallic leaf spring having on its convex surface a layer of electric conducting elastomeric material, means connecting said spring 'to said plate at one point with said elastomeric conducting layers interposed in normal engaging relation at said one point, said spring and plates diverging from said one point, a layer of insulating material interposed between said plate and its conducting layer adjacent to said one point and extending toward a proximate pair of diverging ends of said spring and plate for only a portion of the effective contact length of said spring and plate, and means for pressing at least one end of said spring toward said plate to vary the area of contact between said elastomeric conducting layers.

4. A variable electric resistance device comprising a rigid metallic plate having a ilat surface covered with a layer of graphite-filled silicone rubber, an arcuate leaf spring having a convex surface and connected to said plate at one point with said convex surface facing inwardly, said spring being normally in electric conducting relation with said rubber layer at said one point, a layer of insulating material interposed between said rubber layer and said plate adjacent said point and extending from said point for only a portion of the effective contact area of said layer, and means for pressing at least one end of said spring toward said plate to vary the area of contact of said rubber layer.

5. A variable electric resistance device com.. prising a rigid metallic plate having a ilat surface covered with a layer of electric conducting elastomeric material, an arcuate metallic leaf spring connected at one end to said plate with its convex surface facing inwardly, said spring being in electric conducting relation with elastomeric conducting layer at said one end and diverging from said plate, a layer of insulating material interposed between said plate and said elastomeric layer adjacent the connected end of said spring and extending for only a portion of the length of said spring, and means for pressing the .diverging end of said spring toward said plate to vary the contact area on said elastomeric conducting layer.

6. A variable electric resistance device comprising a rigid metallic plate having a flat surface covered with a layer oi' electric conducting elastomeric material, a pair of arcuate metallic leaf springs each having on its convex surface a layer of electric conducting elastomeric material, means connecting one end of each said spring to said plate with said springs in end-toend relation and with the elastomeric layers on said springs and plates facing inwardly, said springs being connected to said plate at the mutually remote ends and diverging from said plate at their proximate ends ,a layer of insulating material interposed between said plate and its covering layer of elastomeric material adjacent the point of connection of each said spring and extending for only a portion of the length of the associated spring, and means for pressing the diverging proximate ends of said springs toward said plate to vary the area of contact between said elastomeric conducting layers.

7. A variable electric resistance device comprising a base, a pair of resistance plates at least one of which is resilient connected together in -Ewithin said casing, an annular mounting collar -adiustably mounted within said casing for axial movement, and a movable actuating member carried by said mounting collar and disposed to press together the diverging ends of said plates.

9. A variable electric resistance device comprising a hollow cylindrical casing, a pair of resistance plates at least one of which is resilient coated with elastomeric resistance material and 8 connectedtogetherinoveriyingdiversillrelation. means mounting said plates transversely withinsaidcasing.anannularmountingcollar adiustably mounted within said casing for axial s movement. a movably mounted actuating munber including a magnetizable actuator carried by said mounting collar and disposed to pre. together the diverging ends of said plates. and an electromagnet adjustably mounted on laid col-1 m lar in attractive relation to said collar.

JOHNm REFERENCES CITED The following references are of recordA in il 5 leofthlspatcnt:

UNrrnn s'ra'rns Pam'ra Number Name ,Date

1,448,681 Btoekle ---s liar. 18. im go 2,181,565 Huth N0'. 2l. i

Agen! 809. 7. Il 

